Fluorine is the element with highest electronegativity. Due to its size and unique electronic properties, fluorine quite often imparts significantly different (often beneficial) properties to organic molecules. (Chambers 2004; Kirsch 2004) Typically, incorporation of fluorine into molecules results in profound changes in physical and chemical properties of molecules. Fluororganics (i.e., organic compounds with one or more fluoro substituents) have important applications in a wide variety of fields including, but not limited to, material science, agrocultural chemistry and the pharmaceutical industry. (Liebman, Greenberg, and Dolbier 1988).
Significant work has been carried out in the past to incorporate a fluorinated moiety in organic molecules. Trifluoromethyltrimethylsilane (TMS-CF3) is a well known trifluoromethylating reagent. Usefulness of TMS-CF3 has been extensively demonstrated by introducing trifluoromethyl group to transform aldehydes and ketones to trifluoromethylated alcohols. Introducing the trifluoromethyl group at various carbon, sulfur, phosphorus and nitrogen centers has been also demonstrated. (Prakash and Yudin 1997; Singh and Shreeve 2000).
Various fluoride sources, such as tetrabutylammonium fluoride (TBAF), tetrabutylammonium triphenyldifluorosilicate (TBAT), tetramethylammonium fluoride (TMAF) or cesium fluoride, have been used as a catalyst (or initiator) for the trifluoromethylation reaction of different electrophiles. (Singh and Shreeve 2000; Nelson, Owens, and Hiraldo 2001; Petrov 2000; Li, Tang, and Piccirilli 2001; Sevenard et al. 2003; Benayoud et al. 2000; Lin and Jiang 2000). However, these initiators are expensive and moisture sensitive. The most commonly used catalyst for trifluoromethylation using TMS-CF3 is tetrabutylammonium fluoride (TBAF) which typically exists in a hydrated form, e.g., as a trihydrate. TBAF is also available commercially as 1 M solution in THF. Such a solution typically has about 5% water. Attempts to dehydrate TBAF further at higher temperature often leads to production of HF and olefinic byproducts. Without being bound by any theory, it is believed that the presence of water facilitates decomposition of TMSCF3 into CF3H, thereby resulting in a significantly lower or no desired reaction.
Conventional methods for converting simple esters into the corresponding trifluoromethyl ketones are a relatively slow or sluggish process or often results in a low yield of the desired product. The main reason of this failure is the presence of water in the catalyst (TBAF). It is believed that water destroys the key intermediate formed during the reaction, thereby interfering in the catalytic cycle.
Therefore, there is a continuing need for fluorination catalyst or initiator for perfluoroalkylation reaction of organic compounds.